Vol 5 Issue 2 August 2011

New design tool helps ensure quality
in mixes that include high percentages
of recycled asphalt pavement

Increased demand for asphalt and rising construction,

shipping, and manufacturing costs have intensified the push for conservation in the asphalt industry.

 

The University of Nevada-Reno and University of Wisconsin-Madison

are investigating techniques for analyzing the material properties

of asphalt mixtures with high recycled asphalt pavement contents.

 

In small quantities (less than 25%), the asphalt in recycled asphalt pavement (RAP) may not significantly affect the properties of virgin asphalt binders. In quantities higher than 25%, however, the hardened RAP binder may stiffen the mix and alter its mechanical properties. There are no standard procedures routinely used by agencies to separate and test the binder and aggregates of RAP materials.

The binder content of RAP can be easily identified through the extraction process, but measuring the properties of the binder still presents a challenge. Likewise, the gradation of the aggregates in RAP can be easily evaluated through the extraction process; the challenge lies in determining the specific gravity of the RAP aggregates. Again, several techniques have been used but none has emerged as an accepted standard procedure.

Researchers from the University of Wisconsin-Madison (UWM) and University of Nevada-Reno (UNR) are investigating a continuous grade mortar testing approach to determine if the effect of RAP on blended binder properties can be quantified using current Superpave binder testing equipment. Results show that the final binder grade in the mixture is dependent on both the RAP source and the starting fresh binder grade.  Chemical modification of the fresh binder also influences the final binder grade. 

The Asphalt Research Consortium (ARC) continues to work on the proposed analysis procedure, specifically on the characterization of workability properties associated with high-percentage RAP.  Dynamic shear rheometer (DSR) testing to isolate binder viscosity properties is underway.  Fracture characteristics of RAP mixtures are also being explored, with preliminary results showing that RAP has a significant and measurable effect on the fracture properties of virgin binder.

The new binder analysis procedure appears to capture the blended binder properties at low, intermediate and high temperatures and shows promise for replacing chemical extraction and recovery. Perhaps most important, the procedure is less material-dependent than asphalt−aggregate mixture testing and less costly than chemical extraction and recovery. Any laboratory equipped to perform standard Superpave testing can perform the proposed procedure with existing equipment. CLICK HERE to learn more about the design system for high-percentage RAP in hot mix asphalt.  ARC

 

 

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Questions or comments? E-mail us at psebaaly@unr.edu or call 775-784-6565.

 

Please Visit the ARC website to find references and links

to Publications/Conference Proceedings, Presentations/Posters and other useful information.

2011 Petersen Asphalt Research Conference

ARC researchers find an eager

audience for current findings

New tests, models, insights

 

Approximately 140 researchers, highway officials, producers, and others convened in Laramie, Wyoming, July 11 through 13 for the 48th annual Petersen Asphalt Research Conference, hosted by Western Research Institute (WRI).

Current, ongoing research is the theme of the conference. The meeting originated with a few men in a small room and has since grown into an annual international forum. The essential character of the gathering remains the same, however, with researchers presenting their work and peers stepping to the microphone to offer observations, suggestions, and perspectives.

The Petersen Asphalt Research Conference promotes understanding of how asphalt chemistry, physical properties, and interactions affect the performance of asphalt applications throughout their life cycle. This year, the event attracted participants from Sweden, France, The Netherlands, Nigeria, Israel, Canada, Mexico, and throughout the United States.

Asphalt Research Consortium members from Western Research Institute, University of Wisconsin-Madison, University of Rhode Island, Texas A&M University, and ARC collaborators from Delft University of Technology presented on a range of topics. They proposed new insights in asphalt healing, aging, and mechanical properties, either under shear or tension/compression, tying binder chemistry to the properties of asphalt mixtures. They also proposed new models and binder tests to better predict asphalt field performance.

For almost 50 years, the fundamental and applied research presented at the conference has led to advancements in the specification and performance of petroleum asphalts and ultimately to safer, longer-lasting, and more cost-effective highways throughout the world. To view the program and abstracts of the presentations, CLICK HERE.  ARC